Almost everyone in a band I've ever met has been nice. They usually just seem really appreciative that you care about their music and bothered to walk up to their merch table/bus/barstool to tell them so. And it's pretty fucking easy to meet bands without really trying, so I'm not gonna sit here and make a list - I've met way, way, way too many musicians I admire for that.

My favorite encounters have been with Brann Dailor and Mikael Åkerfeldt, probably.

EDIT: Oh, and honorable mention to Phil McSorley, who was a wonderful and candid interviewee, but whom I unfortunately had to interview by phone thanks to geographical complications.

John Cafiero(Osaka Pop Star)Nice guy,i took a pic with him cause i felt bad for him cause his band really sucks ass.
Billy Zoom (X)Nice at first then got all pissy with me cause i asked about another member of X.

Joe Esclante(The Vandals)My favorite republican. He told to jump over a gate to take a pic. Also cool on the radio when i used to call in.
Joey Bondange(Narcoleptic Youth)Dude! A total Badass!

Mike Watt(Minutemen,fIREHOSE)He was so excited when i asked for his picture at warped tour. No other "punx as fuck" poser knew who this legend was.

Bay Cortez(Possessed,Sadistic Intent)HA! Nice guy for letting me hang out in his store and sold me an Anal Cunt cd. He still gave me a discount card for spending 60 bux.
LandPhil(Municipal Waste,Cannabis Corpse)He was nice enough to let me take 2 pics with him since the first one was all fucked up. Really nice guy. Totally stoned.
Joel Grind(Toxic Holocaust,Tiger Junkies)I pointed at him,he pointed at me we smiled as we walked away. My best gay moment.

Alex Webster(Cannibal Corpse)Really nice guy who took a pic with my friend and talked to us for a few
Neil Turbin(Anthrax,Deathriders)Really nice guy and gets happy when u talk to him.

Katon W.De Pena(Hirax)Nice dude,very nice.

John Kevill(Warbringer)TOTAL COOL!
Mel Mongeon(Fuck The Facts)She was kinda like wtf about me but eh she was pregnant so i dont mind.

Marc Bourgon(Fuck The Facts)Nice guy,gave me free stickers.

Chance Garnett(Skeletonwitch)Badass singer,badass dude

Phil Campbell (Motörhead)He was ok i guess. Not nice,not mean

Gio(Meciless Death)-Too wasted,too funny. Nice overall

Alladin(Bonded By Blood)-Nice enough to take a pic with,he will be missed!

Anthony Vasquez(Fueled By Fire)-Total Dick

Konan(Exmortus,RattleheaD)Let me have a free shirt if i let my buddy hit me in the face. Nice guy!

Most of the bands I have met are really nice.. Lamb of God, Trivium, Dragonforce, Anthra, Atreyu, Motion City Soundtrack, Down/Pantera, Suffocation, Mucc, Horse The Band, Annihilator, Bleeding Through, Hatebreed, Man Must Die..

Only assholes I have encountered really are Carcass, they cancelled their signing at Graspop, but then when we saw them come out of the VIP entrance into the festival area Michael Amott refused to shake one of my friends hands and Jeff Walker ignored me when I asked for a photo.. Obituary and Bullet For My Valentine were ok, just sorta indifferent to the whole thing..

Derek Kerswill from Unearth is really cool, me and a buddy had a few drinks with him
Cannibal Corpse, Machine Head, and Motorhead(except i didn't meet all memebrs ) are probably the nicest bands i've met, and All That Remains.
When I met Ivan from 5FDP he was really nice...

as for dicks...hmmm
Can't think of any right now..
i haven't met anyone from Bodom, buy I can just tell that they would be dicks, I know someone who met Alexi and he said he was a complete asshole